Study viral and cellular aspects of leukemic transformation of T lymphocytes in vitro by thumus reticuloepithelial cells. The three aspects of leukemogenesis to be studied in vitro shall be: analysis of the role of retraviruses; identification of target lymphocytes and the mechanism of their susceptibility to leukemic transformation; and purification of different types of thymus reticuloepithelial cells and their function in leukemia induction.